The invention relates to the field of closed-loop, refrigerant-based, direct expansion, heating and cooling systems which encounter one or more of significant system component height differentials, particularly significant compressor and condenser height differentials, and significant system refrigerant fluid transport line distances. The invention is of particular advantage in direct expansion heating and cooling systems, wherein a refrigerant fluid, such as R-22, or the like, is circulated by a compressor through heat conductive tubing, typically copper tubing, located below ground, to acquire heat from the ground in the winter and to reject heat into the ground in the summer. This direct expansion system in-ground heat exchange system typically eliminates the need for the outdoor air heat exchange unit in a conventional air-source heat pump system, and eliminates the need for an open or a closed loop of circulating water in a conventional water source heat pump system, thereby increasing overall system operational efficiencies. Direct expansion systems are typically installed via a series of in-ground heat exchange tubes, buried about 4 to 6 feet deep in a horizontal array, or via an array of vertical or angled tubing buried about 50 to 100 feet deep. Generally, most in-ground heat exchange tubing is designed to be within a distance of about 50 to 100 feet from the compressor unit. The present invention utilized in a direct expansion system will permit deep well, beyond 50 to 100 feet, applications, and will additionally permit the location of in-ground heat exchange tubing to be located significant distances, beyond 50 to 100 feet, from the compressor unit.
A compressor is used in all direct expansion, refrigerant-based, heat transfer systems. The compressor takes an incoming heat-laden refrigerant vapor, from a larger sized refrigerant transport line, and compresses the vapor into a smaller sized refrigerant transport line, thereby condensing the existing heat into a smaller area and increasing the temperature of the refrigerant vapor. The heated refrigerant vapor is circulated, via force of the compressor, to a cooler heat exchange medium, termed the condenser, where heat is removed from the refrigerant. As the heat is removed, the cooled refrigerant condenses into a liquid state. The liquid refrigerant is then directed, via a liquid transport line, to an expansion valve, which, via expanding and lowering the pressure of the refrigerant, effectively causes the refrigerant to expand into a cooler mostly vapor state. The cooled vapor state refrigerant is transported, again by means of force of the compressor operation, via a line of larger diameter than the liquid line, and is circulated to a heat source area, termed the evaporator, to acquire heat which raises the temperature of the refrigerant vapor. The heated vaporized refrigerant, having acquired heat from the desired source, is pulled into the compressor by its suction operation, where the process is repeated. This provides an effective means of heat transfer.
Since compressors are primarily designed to act as compressors, even when there is a modest elevation differential, such as 10 to 25 feet, between the compressor and the condenser, such that a refrigerant liquid elevation load is placed on the compressor which is now required to perform increased pumping work, system operational efficiencies are noticeably impaired. Beyond 50 to 100 feet, system operational efficiencies are materially impaired. For example, via testing in a vertical in-ground heat exchange direct expansion refrigerant-based geothermal heating/cooling system, such as that described in B. Ryland Wiggs' U.S. Pat. No. 5,623,986, the disclosure of which is incorporated herein by reference, testing has shown that, when operating in the cooling mode, where the in-ground heat exchange coils are acting as the condenser, system operational efficiencies decrease as the depth of the in-ground heat exchanger increases. This is due to the increasing head pressure of the refrigerant liquid on its way up from an elevation materially lower than the compressor, as compressors are not designed to operate as liquid elevation pumps. The same is true in a horizontal application, such as that described in B. Ryland Wiggs U.S. Pat. No. 5,946,928, the disclosure of which is incorporated herein by reference, where the horizontal in-ground heat exchanger is at a depth materially below the compressor when operating in a cooling mode, or where the height of the in-ground heat exchanger is materially above the compressor when operating in a heating mode, such as where the in-ground system is on a hill above the system's compressor in the house.
Since most refrigerant heat pump systems do not operate under constant conditions, most utilize self-adjusting expansion valves in both the heating and the cooling modes. These valves operate at their peak efficiencies when they are close, generally within about two feet, to the heat exchange means operating as the evaporator, and the greater the distance, the lower their operational efficiency as these valves become more prone to hunting rather than to maintaining an optimum setting. While the primary object of the invention is to permit one or both of a deep well and an extended refrigerant line length in a direct expansion system application, placement of the refrigerant pump in the system's liquid line prior to the expansion valve will also assist in maintaining a preferable uniform refrigerant flow to the expansion valve.
Regarding refrigerant pumps, although some strictly cooling mode refrigerant systems utilize pumps to modestly increase the otherwise normal operational pressure of the liquid refrigerant flowing into the expansion valve primarily for the purpose of helping to suppress flash gas, the most common historical utilization of refrigerant pumps are for use in refrigerant recovery systems. These recovery systems are used to pump refrigerant out of a closed-loop system into a storage container so as to permit repairs or service to the system. Once the servicing is completed, the refrigerant is returned to the closed-loop system. This refrigerant recovery system inhibits the wasting of refrigerant fluids, and helps to protect the earth's ozone layer from certain refrigerants' harmful effects if they were simply released into the atmosphere.